1. Field of the Invention
The present invention relates in general to a wideband impulse transmitting/receiving antenna for use with communication systems employing electromagnetic impulses, such as, UWB (Ultra Wideband) communications. More specifically, the present invention relates to a miniaturized UWB microstrip antenna having excellent wideband characteristics by changing the notch structure of a main radiating element and a sub-radiating element connected to the main radiating element.
2. Description of the Related Art
UWB uses pulses which have the attribute of being spread over a frequency range measured in 3.1-10.6 gigahertz (GHz) for transmitting digital data as far as 10 m-1 km.
As already known, impulse radio communications, unlike existing narrowband communications, use an ultra-wideband frequency band and transmit high-speed data consuming much power. To commercialize the impulse radio communication system for a mobile communication terminal, however, a small-sized antenna has to be used.
A related art UWB antenna for transmitting/receiving impulses mainly has been used for radar feed, so its important features of radiating pattern are high power, wide bandwidth, high gain, and low sidelobe. In effect, there were few studies being done on impulse antennas for use with personal mobile communication terminals.
The following will explain related art wideband antennas.
FIG. 1 illustrates an ultra-wideband antenna disclosed in U.S. Pat. No. 5,428,364. This type of antenna requires an impedance taper featuring wide bandwidth impedance matching, in order to secure desired radiation patterns over every range of frequencies and to transmit electromagnetic energy inputted from a source without loss. Also, a slot line impedance taper is used in a matching circuit for wideband matching, so the size of the antenna has to be increased in proportion to a usable frequency range.
FIG. 2 illustrates a single-layer wideband antenna using a stub, disclosed in Korean Pat. No. 2002-73660. For this type of antenna, an open or short stub is attached to a radiating patch to overcome weakness of an existing patch antenna, and as a result, excellent wideband impedance matching characteristics and wideband characteristics are obtained. However, the antenna could not accommodate the UWB waveform, and the patch antenna, being a single patch antenna by nature, is incapable of realizing omni-directional characteristics of antennas. In addition, when mounted in small-sized mobile communication equipment, the antenna's directivity interferes with smooth and proper communication, and thus, at least two antennas are required.
FIG. 3 illustrates a print dipole antenna with wideband characteristics by constructing a matching circuit with more than one open stub on a microstrip line, disclosed in Japanese Pat. No. 5-3726. The print dipole antenna has the matching circuit on a signal line, so it occupies more space than necessary when designing an antenna combined with the dielectric substrate. It is practically impossible to implement a wideband matching circuit having a bandwidth greater than 3:1 in a relatively low (less than 5 GHz) frequency domain. Also, the disclosed antenna has a dual plane structure and thus, process cost thereof is higher than a single plane antenna.
FIG. 4 illustrates an antenna disclosed in Europe Pat. No. WO 02/13313 A2. According to the disclosure, a large planar conductive plate and a small planer conductive plate inserted into an oval-shaped slot are formed in the large element. The suggested antenna size is 2.72×1.83 cm including a radiating slot, which is 8 times bigger than the antenna size of an embodiment of the present invention.
FIG. 5 illustrates an antenna disclosed in U.S. Pat. No. 6,351,246 B1, titled “Planer ultra wide band antenna with integrated electronics”. According to the disclosed antenna, a difference signal is applied feed points, and a resistor is situated between a pair of radiating balance elements to improve voltage standing wave ratio (VSWR) of low frequency. Although this type of antenna has electric elements to meet the requirements of pulse communications in a desired frequency range, it is not proper to be miniaturized. Thus, the practicability of the antenna is basically limited. Moreover, because the resistor is employed in order to improve the VSWR in a low frequency range, it is not easy to maintain high reliability of the antenna.